Fine structure of steroidogenic cells of a primate cutaneous organ

Trafficking of bdelloid rotifer late embryogenesis abundant proteins

The bdelloid rotifer Adineta ricciae is an asexual microinvertebrate that can survive desiccation by entering an ametabolic state known as anhydrobiosis. Two late embryogenesis abundant (LEA) proteins, ArLEA1A and ArLEA1B, have been hypothesized to contribute to desiccation tolerance in these organisms, since in vitro assays suggest that ArLEA1A and ArLEA1B stabilize desiccation-sensitive proteins and membranes, respectively. To examine their functions in vivo, it is important to analyse the cellular distribution of the bdelloid LEA proteins. Bioinformatics predicted their translocation into the endoplasmic reticulum (ER) via an N-terminal ER translocation signal and persistence in the same compartment via a variant C-terminal retention signal sequence ATEL. We assessed the localization of LEA proteins in bdelloids and in a mammalian cell model. The function of the N-terminal sequence of ArLEA1A and ArLEA1B in mediating ER translocation was verified, but our data showed that, unlike classical ER-retention signals, ATEL allows progression from the ER to the Golgi and limited secretion of the proteins into the extracellular medium. These results suggest that the N-terminal ER translocation signal and C-terminal ATEL sequence act together to regulate the distribution of rotifer LEA proteins within intracellular vesicular compartments, as well as the extracellular space. We speculate that this mechanism allows a small number of LEA proteins to offer protection to a large number of desiccation-sensitive molecules and structures both inside and outside cells in the bdelloid rotifer.

Chapter 6: cubic membranes the missing dimension of cell membrane organization

Biological membranes are among the most fascinating assemblies of biomolecules: a bilayer less than 10 nm thick, composed of rather small lipid molecules that are held together simply by noncovalent forces, defines the cell and discriminates between “inside” and “outside”, survival, and death. Intracellular compartmentalization—governed by biomembranes as well—is a characteristic feature of eukaryotic cells, which allows them to fulfill multiple and highly specialized anabolic and catabolic functions in strictly controlled environments. Although cellular membranes are generally visualized as flat sheets or closely folded isolated objects, multiple observations also demonstrate that membranes may fold into “unusual”, highly organized structures with 2D or 3D periodicity. The obvious correlation of highly convoluted membrane organizations with pathological cellular states, for example, as a consequence of viral infection, deserves close consideration. However, knowledge about formation and function of these highly organized 3D periodic membrane structures is scarce, primarily due to the lack of appropriate techniques for their analysis in vivo. Currently, the only direct way to characterize cellular membrane architecture is by transmission electron microscopy (TEM). However, deciphering the spatial architecture solely based on two-dimensionally projected TEM images is a challenging task and prone to artifacts. In this review, we will provide an update on the current progress in identifying and analyzing 3D membrane architectures in biological systems, with a special focus on membranes with cubic symmetry, and their potential role in physiological and pathophysiological conditions. Proteomics and lipidomics approaches in defined experimental cell systems may prove instrumental to understand formation and function of 3D membrane morphologies.

Genetic and structural analysis of Hmg2p-induced endoplasmic reticulum remodeling in Saccharomyces cerevisiae

The endoplasmic reticulum (ER) is highly plastic, and increased expression of distinct single ER-resident membrane proteins, such as HMG-CoA reductase (HMGR), can induce a dramatic restructuring of ER membranes into highly organized arrays. Studies on the ER-remodeling behavior of the two yeast HMGR isozymes, Hmg1p and Hmg2p, suggest that they could be mechanistically distinct. We examined the features of Hmg2p required to generate its characteristic structures, and we found that the molecular requirements are similar to those of Hmg1p. However, the structures generated by Hmg1p and Hmg2p have distinct cell biological features determined by the transmembrane regions of the proteins. In parallel, we conducted a genetic screen to identify HER genes (required for Hmg2p-induced ER Remodeling), further confirming that the mechanisms of membrane reorganization by these two proteins are distinct because most of the HER genes were required for Hmg2p but not Hmg1p-induced ER remodeling. One of the HER genes identified was PSD1, which encodes the phospholipid biosynthetic enzyme phosphatidylserine decarboxylase. This direct connection to phospholipid biosynthesis prompted a more detailed examination of the effects of Hmg2p on phospholipid mutants and composition. Our analysis revealed that overexpression of Hmg2p caused significant and specific growth defects in nulls of the methylation pathway for phosphatidylcholine biosynthesis that includes the Psd1p enzyme. Furthermore, increased expression of Hmg2p altered the composition of cellular phospholipids in a manner that implied a role for PSD1. These phospholipid effects, unlike Hmg2p-induced ER remodeling, required the enzymatic activity of Hmg2p. Together, our results indicate that, although related, Hmg2p- and Hmg1p-induced ER remodeling are mechanistically distinct.

Receptor-mediated transport of IgG across the intestinal epithelium of the neonatal rat

The absorptive epithelium of the neonatal rat is developmentally specialized to transfer maternal immunoglobulin G (IgG) intact to the circulation while other milk protein are digested. The epithelial cells of the duodenum and proximal jejunum which are responsible for IgG transfer represent a particular striking experimental model for study of receptor-mediated intracellular transport. Receptors located on the luminal plasma membrane selectively bind the Fc region of IgG. The IgG enters the cell by constitutive endocytosis within coated vesicles and is then released at the basolateral plasma membrane. Morphological evidence supports a model in which IgG crosses the cell as a ligand-receptor complex that dissociates only on exposure to a pH 7.4 environment found at the basolateral cell surface. Although uptake of IgG at the luminal plasma membrane is highly selective, small but significant amounts of other proteins enter the cell apparently non-selectively. Nevertheless, these latter proteins are not transferred across the cell. Double-tracer experiments indicate that IgG and these other proteins enter the cell simultaneously within the same endocytic vesicles, but that non-membrane-bound proteins are removed from the IgG transport pathway by an as yet poorly defined mechanism and sequestered within small apical vacuoles and lysosomes.

Cubic membranes: a legend beyond the Flatland* of cell membrane organization

Cubic membranes represent highly curved, three-dimensional nanoperiodic structures that correspond to mathematically well defined triply periodic minimal surfaces. Although they have been observed in numerous cell types and under different conditions, particularly in stressed, diseased, or virally infected cells, knowledge about the formation and function of nonlamellar, cubic structures in biological systems is scarce, and research so far is restricted to the descriptive level. We show that the “organized smooth endoplasmic reticulum” (OSER; Snapp, E.L., R.S. Hegde, M. Francolini, F. Lombardo, S. Colombo, E. Pedrazzini, N. Borgese, and J. Lippincott-Schwartz. 2003. J. Cell Biol. 163:257–269), which is formed in response to elevated levels of specific membrane-resident proteins, is actually the two-dimensional representation of two subtypes of cubic membrane morphology. Controlled OSER induction may thus provide, for the first time, a valuable tool to study cubic membrane formation and function at the molecular level.

The dynamic ER: experimental approaches and current questions

The endoplasmic reticulum (ER) is an extremely plastic and dynamic organelle. Its size and shape can undergo drastic changes to meet changing demands for ER-related functions, or as a response to drugs or pathogens. Because of the ER's key functions in protein and lipid synthesis, this organelle is a hotbed of detailed molecular analysis.

Crystalloids in the excretory ducts of the accessory submandibular gland of the long-winged bat, Miniopterus magnator

Cytoplasmic crystalloids are abundant in the excretory ducts of the accessory submandibular gland of the long-winged bat, Miniopterus magnator. The crystalloids, which always lack a membranous enclosure, may have an intricate silhouette. They consist of parallel linear densities with a 12.5 nm periodicity. These densities actually may be thin-walled tubules. In some crystalloids, intersecting subcrystalloids produce a complex pattern of decussate densities. In a few rare instances, continuities were detected between a crystalloid and a smooth-surfaced cisternal element. In other mammalian species, similar crystalloids connected to smooth endoplasmic reticulum play a role in steroid metabolism. We postulate that the ductular crystalloids in M. magnator might be involved in production of a factor that influences mating behavior.

Different subcellular localization of Saccharomyces cerevisiae HMG-CoA reductase isozymes at elevated levels corresponds to distinct endoplasmic reticulum membrane proliferations

In all eucaryotic cell types analyzed, proliferations of the endoplasmic reticulum (ER) can be induced by increasing the levels of certain integral ER proteins. One of the best characterized of these proteins is HMG-CoA reductase, which catalyzes the rate-limiting step in sterol biosynthesis. We have investigated the subcellular distributions of the two HMG-CoA reductase isozymes in Saccharomyces cerevisiae and the types of ER proliferations that arise in response to elevated levels of each isozyme. At endogenous expression levels, Hmg1p and Hmg2p were both primarily localized in the nuclear envelope. However, at increased levels, the isozymes displayed distinct subcellular localization patterns in which each isozyme was predominantly localized in a different region of the ER. Specifically, increased levels of Hmg1p were concentrated in the nuclear envelope, whereas increased levels of Hmg2p were concentrated in the peripheral ER. In addition, an Hmg2p chimeric protein containing a 77-amino acid lumenal segment from Hmg1p was localized in a pattern that resembled that of Hmg1p when expressed at increased levels. Reflecting their different subcellular distributions, elevated levels of Hmg1p and Hmg2p induced sets of ER membrane proliferations with distinct morphologies. The ER membrane protein, Sec61p, was localized in the membranes induced by both Hmg1p and Hmg2p green fluorescent protein (GFP) fusions. In contrast, the lumenal ER protein, Kar2p, was present in Hmg1p:GFP membranes, but only rarely in Hmg2p:GFP membranes. These results indicated that the membranes synthesized in response to Hmg1p and Hmg2p were derived from the ER, but that the membranes were not identical in protein composition. We determined that the different types of ER proliferations were not simply due to quantitative differences in protein amounts or to the different half-lives of the two isozymes. It is possible that the specific distributions of the two yeast HMG-CoA reductase isozymes and their corresponding membrane proliferations may reveal regions of the ER that are specialized for certain branches of the sterol biosynthetic pathway.

From entangled membranes to eclectic morphologies: cubic membranes as subcellular space organizers

The identification of evolutionary conserved membrane morphologies whose architecture is governed by cubic symmetry--cubic membranes--adds a new dimension to cell membrane functions and, perspicuously, to their role in subcellular space organization. Through analysis of electron micrographs, three families of cubic membranes have been unequivocally identified in which one or more (parallel) membranes, described by periodic cubic surfaces, partition space into two or more independent, albeit convoluted, subspaces of membrane potential determined dimensions. The choice of a particular cubic symmetry is suggested to be due to its activity. Here the architecture and function of multiple (> or = 3) subspace organization in classical membrane bound organelles is addressed. As it can be precisely determined with cubic membranes suggests that they can be employed as a reference morphology.

Regulated degradation of HMG-CoA reductase, an integral membrane protein of the endoplasmic reticulum, in yeast

Numerous integral membrane proteins are degraded in the mammalian ER. HMG-CoA reductase (HMG-R), a key enzyme in the mevalonate pathway by which isoprenoids and sterols are synthesized, is one substrate of ER degradation. The degradation of HMG-R is modulated by feedback signals from the mevalonate pathway. We investigated the role of regulated degradation of the two isozymes of HMG-R, Hmg1p and Hmg2p, in the physiology of Saccharomyces cerevisiae. Hmg1p was quite stable, whereas Hmg2p was rapidly degraded. Degradation of Hmg2p proceeded independently of vacuolar proteases or secretory traffic, indicating that Hmg2p degradation occurred at the ER. Hmg2p stability was strongly affected by modulation of the mevalonate pathway through pharmacological or genetic means. Decreased mevalonate pathway flux resulted in decreased degradation of Hmg2p. One signal for degradation of Hmg2p was a nonsterol, mevalonate-derived molecule produced before the synthesis of squalene. Genetic evidence indicated that a farnesylated protein may also be necessary for Hmg2p degradation. Studies with reporter genes demonstrated that the stability of each isozyme was determined by its noncatalytic NH2-terminal domain. Our data show that ER protein degradation is widely conserved among eukaryotes, and that feedback control of HMG-R degradation is an ancient paradigm of regulation.

The G protein of vesicular stomatitis virus has free access into and egress from the smooth endoplasmic reticulum of UT-1 cells

We have investigated the role of the smooth endoplasmic reticulum (SER) of UT-1 cells in the biogenesis of the glycoprotein (G) of vesicular stomatitis virus (VSV). Using immunofluorescence microscopy, we observed the wild type G protein in the SER of infected cells. When these cells were infected with the mutant VSV strain ts045, the G protein was unable to reach the Golgi apparatus at 40 degrees C, but was able to exit the rough endoplasmic reticulum (RER) and accumulate in the SER. Ribophorin II, a RER marker, remained excluded from the SER during the viral infection, ruling out the possibility that the infection had destroyed the separate identities of these two organelles. Thus, the mechanism that results in the retention of this mutant glycoprotein in the ER at 39.9 degrees C does not limit its lateral mobility within the ER system. We have also localized GRP78/BiP to the SER of UT-1 cells indicating that other mutant proteins may also have access to this organelle. Upon incubation at 32 degrees C, the mutant G protein was able to leave the SER and move to the Golgi apparatus. To measure how rapidly this transfer occurs, we assayed the conversion of the G protein's N-linked oligosaccharides from endoglycosidase H-sensitive to endoglycosidase H-resistant forms. After a 5-min lag, transport of the G protein followed first order kinetics (t1/2 = 15 min). In contrast, no lag was seen in the transport of G protein that had accumulated in the RER of control UT-1 cells lacking extensive SER. In these cells, the transport of G protein also exhibited first order kinetics (t1/2 = 17 min). Possible implications of this lag are discussed.

Structure and development of iridescent butterfly scales: Lattices and laminae

Iridescent butterfly scales are structurally colored, relying upon the interaction of light with detailed architecture to produce their color. In some iridescent scales, the reflective elements are contained within the body of the scale and come in two basic forms, lattices that produce diffraction colors (analogous to those produced by opal), and stacks of laminae that produce thin-film interference colors (analogous to those produced by soap or oil films). Both structures are remarkably complex and precise, yet each is only part of the total edifice built by the cell that makes the scale. To understand better how a cell can produce lattices or thin-film laminae, I studied the development of iridescent scales from two lycaenid butterflies. The presence of diffraction and thin-film scales in the same family (and in some cases on the same individual) suggests that the two types must be developmentally related; yet these results yield no clear explanation as to how. The diffraction lattice appears to be shaped within the boundaries of the scale cell by means of a convoluted series of membranes in which the smooth endoplasmic reticulum plays an important part. The thin-film interference laminae appear to result from the condensation of a network of filaments and tubes secreted outside the boundaries of the cell. This paper outlines the developmental histories of both types of scale and discusses the developmental implications of the mechanisms by which they form.

Unusual configurations of endoplasmic reticulum in pinealocytes of the Djungarian hamster (Phodopus sungorus)

Ultrastructural observations of the pineal gland of Phodopus sungorus revealed different morphological forms of endoplasmic reticulum. These included crystalloids composed of 200A-wide tubules with an intervening space of 200A and connected at right angles to form a rectangular lattice; complexes of undulating 500A-wide tubules in an electron-dense cytoplasmic matrix; and stacks of flattened cisternae covered with granular electron-dense material. All these structures are continuous with the surrounding endoplasmic reticulum. Frequently one structure is directly connected with another. The exact function of these structures derived from the endoplasmic reticulum is still unclear, but they can be assumed to be morphological features of augmented secretory activity.

Crystalloid formation in Leydig cells of rats (Rattus fuscipes). An ultrastructural and hormonal study

The ultrastructure of Leydig cells in a seasonally breeding rodent, Rattus fuscipes, was studied in the breeding and non-breeding season and compared with Leydig cell morphology after suppression of gonadotrophin secretion induced by hypophysectomy or chronic administration of testosterone. Serum luteinizing hormone (LH) and testosterone (T) were measured and in-vitro T production by testes was assessed by stimulation with human chorionic gonadotrophin (hCG). In non-breeding wild-trapped rats and rats with experimental suppression of gonadotrophins, the Leydig cells were atrophied and exhibited variable amounts of cytoplasmic lipid and crystalloid inclusions, the latter commonly dominating the cytoplasmic area. Compared with fertile rats, serum LH and hCG-stimulated T production of experimentally regressed rats was significantly reduced, confirming structural features indicative of Leydig cell inactivity. Atrophy of Leydig cell nuclei was accompanied by the formation of unusual intranuclear vesicles sometimes containing small crystalloids. Ultrastructural analysis suggested transfer of the vesicles to the cytoplasm where their unification gave rise to much larger crystalloid bodies. Crystalloids occurred when serum LH was depressed and with either full (T treatment) or arrested spermatogenesis (hypophysectomy) suggesting that their formation is governed by pituitary function and is not dependent upon the degree of spermatogenic activity.

Hydroxymethylglutaryl-coenzyme A reductase-containing hepatocytes are distributed periportally in normal and mevinolin-treated rat livers

Mevinolin is a potent inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoA reductase; EC 1.1.1.34), an enzyme that catalyzes the rate-limiting step in cholesterol biosynthesis. We have been studying the hepatic distribution of reductase with immunofluorescence microscopy and liver ultrastructure with electron microscopy in normal and drug-treated rats. In control animals, only about 20% of the hepatocytes were reductase positive. These cells were localized in the periportal lobular zones. The numbers of positive hepatocytes in animals given mevinolin or cholestyramine (or both) were directly proportional to the activities of the HMG-CoA reductase determined biochemically. This induction of HMG-CoA reductase immunofluorescence was centered periportally. Rats given 0.075% mevinolin alone had a homogeneous distribution of reductase staining in their hepatocyte cytoplasm, whereas a combination of 0.25% mevinolin and 3% cholestyramine caused a 150-fold increase in enzyme activity and induced prominent juxtanuclear immunofluorescent globules of HMG-CoA reductase in all hepatocytes. With electron microscopy, these bodies were composed of tightly packed stacks of smooth endoplasmic reticulum cysternae and aggregates of branched smooth endoplasmic reticulum tubules. Our data suggest that a subpopulation of periportal rat hepatocytes may be uniquely specialized for cholesterol synthesis.

The differentiation of Leydig cells, steroidogenesis, and the spermatogenetic wave in the testis of Necturus maculosus

The study of seminiferous tubule--Leydig cell interactions in relation to specific germ cell stages during the cycle of the seminiferous epithelium is extremely difficult in most mammalian species due to the continual presence of different spermatogenetic stages in the testis from the onset of puberty. The problem is also compounded by the uniform distribution of both seminiferous tubules and interstitial tissue throughout the entire testis. This difficulty can be circumvented, however, by studying certain species where there is a topographical distribution of germ cell stages within the testis. The urodele amphibian Necturus maculosus exhibits a breeding cycle during which a longitudinal wave of spermatogenesis occurs along the length of the testis, resulting in a spatial and temporal segregation of differentiating germ cells. Moreover, this topographical pattern of spermatogenesis is also reflected in the degree of development of adjacent Leydig cells. This anatomical arrangement allows distinct testicular regions to be obtained using a dissecting microscope. The isolated zones, containing germ cells and Leydig cells in various stages of development, were analyzed for 17 alpha-hydroxylase, C-17,20-lyase, and aromatase activities (key enzymes for the synthesis of androgens and estrogen), estrogen binding, and cytochrome P-450 content. Functional parameters were then correlated with the morphology of Leydig cells in the various zones observed by both light and electron microscopy. It was found that there existed a distinct correlation between the state of differentiation of the leydig cells, their steroidogenic potential, and the distribution of estrogen receptors. These results in Necturus indicate indicate in this species, at least, the steroidal microenvironment of different germ cell associations may be quite specific.

Identification of a cholesterol-regulated 53,000-dalton cytosolic protein in UT-1 cells and cloning of its cDNA

UT-1 cells, a clone of Chinese hamster ovary (CHO) cells, have a 100- to 1,000-fold elevation in the amount of 3-hydroxy-3-methylglutaryl CoA reductase and therefore grow in the presence of compactin, an inhibitor of reductase. In this paper, we report that UT-1 cells also have a markedly increased amount of another protein with a Mr of 53,000 and an isoelectric point of approximately equal to 6. Whereas the reductase is an enzyme of the endoplasmic reticulum, the 53,000-dalton protein (termed the "53k" protein) is in the cytosol. It is not precipitated by an antireductase antibody. Synthesis of the 53k protein, like that of the reductase, is suppressed when UT-1 cells are incubated with plasma low density lipoprotein (LDL). We prepared a library of recombinant plasmids containing double-stranded cDNAs from UT-1 cells. Using differential colony hybridization, we identified recombinant plasmids containing double-stranded cDNA inserts encoding mRNAs expressed at high levels in UT-1 cells as compared with CHO cells. One of the plasmids, designated p53k-3, contained a 0.97-kilobase double-stranded cDNA that hybridized to a 3.8-kilobase mRNA. When translated in vitro, this 3.8-kilobase mRNA directed the synthesis of a protein identical to the cellular 53k protein as determined by two-dimensional gel electrophoresis. Hybridization studies showed that the mRNA for the 53k protein was present in much larger amounts in UT-1 cells than in parental CHO cells. In both cell types, the content of this mRNA decreased markedly when the cells were incubated with LDL. Although the function of the 53k protein is not known, circumstantial evidence suggests that it may represent cytosolic 3-hydroxy-3-methylglutaryl CoA synthase, the enzyme preceeding the reductase in the cholesterol biosynthetic pathway. The current data indicate that the synthesis of at least two proteins, the reductase and the 53k protein, are induced to high levels in compactin-resistant UT-1 cells and that the synthesis of both is suppressed coordinately by LDL.

Appearance of crystalloid endoplasmic reticulum in compactin-resistant Chinese hamster cells with a 500-fold increase in 3-hydroxy-3-methylglutaryl-coenzyme A reductase

We have developed a line of Chinese hamster ovary cells with a 500-fold increase in 3-hydroxy-3-methylglutaryl-coenzyme A reductase, the membrane-bound enzyme that controls cholesterol synthesis. This line, designated (UT-1, was obtained by stepwise adaptation of cells to growth in increasing concentrations of compactin, a competitive inhibitor of reductase. Reductase accounts for approximately 2% of total cell protein in UT-1 cells, as calculated from enzyme specific activity and by immunoprecipitation of reductase after growth of cells in [35S]methionine. After solubilization in the presence of the protease inhibitor leupeptin and electrophoresis in NaDodSO4/polyacrylamide gels, reductase subunits from UT-1 cells were visualized by immunoblotting as a single band (Mr = 62,000). To accommodate the increased amounts of reductase, UT-1 cells developed marked proliferation of tubular smooth endoplasmic reticulum (ER) membranes, as revealed by immunofluorescence and electron microscopy. The ER tubules were packed in crystalloid hexagonal arrays. When UT-1 cells were incubated with low density lipoprotein, reductase activity was suppressed by 90% in 12 hr and the crystalloid ER disappeared. UT-1 cells should be useful for studies of the regulation of reductase and also for studies of the synthesis and degradation of smooth ER.

Specific paracrystalline structures of rough endoplasmic reticulum in the follicular (stellate) cells of the dog adenohypophysis

The fine structure of follicular cells of the adenohypophysis was examined in fetal, neonatal, and adult beagle dogs. Prior to birth, undifferentiated follicular cells are common. At birth mature cells that form follicles are routinely encountered. The fine structural appearance of follicular cells is unchanged between birth and adulthood. Follicular cells of puppies and adults are, however, distinguished by the presence of unusual complexes within distended cisternae of the rough endoplasmic reticulum. These complexes vary greatly in morphology, some appear as a maze of interconnecting tubules while others show a highly organized paracrystalline configuration. The presence of these paracrystalloid structures in follicular cells supports the view that they represent a distinct pituitary cell type.

Morphology of the granular secretory glands in skin of poison-dart frogs (Dendrobatidae)

The granular glands of nine species of dendrobatid frogs were examined using light and electron microscopy. The glands are surrounded by a discontinuous layer of smooth muscle cells. Within the glands proper the secretory cells form a true syncytium. Multiple flattened nuclei lie at the periphery of the gland. The peripheral cytoplasm also contains mitochondria, rough surfaced endoplasmic reticulum, the Golgi apparatus, and an abundance of smooth endoplasmic reticulum. Centrally, most of the gland is filled with membrane-bound granules surrounded by amorphous cytoplasm. Few other organelles are found in this region. Early in the secretory cycle, the central part of the gland is filled with flocculent material which appears to be progressively partitioned off by membranes to form the droplet anlage. As granules form, the structure of the contents becomes progressively more vesicular. Dense vesicles, which bud off from the Golgi apparatus, fuse with the granular membrane during the development of granules, and might contain enzymes involved in toxin synthesis. The granules at this point resemble multivesicular bodies. Their structure is similar in all species of dendrobatid frogs even though the different frogs secrete substances of different chemical structure and toxicity.

Crystalloid configuration in the adrenal cortex of the Siamese tree shrew (Tupaia glis)

Crystalloids of what appear to be smooth reticulum have been observed in the zona fasciculata and zona reticularis in both the stressed and nonstressed adrenal gland of the Siamese tree shrew (Tupaia glis). No crystalloids are observed in the zona glomerulosa. Similar crystalloids have been described in other steroid-secreting organs, including the antebrachial organ of the lemur (Lemur catta), the parotoid gland of Bufo alvarius and in sebaceous gland cells of the Galagos and Macaques. Moreover, the crystalloids in the present investigation resemble the paracrystalline arrays of smooth reticulum present in the adrenal cortex of the fetal guinea pig. The crystalloids show much variation in degree of organization, sometimes appearing as wavy tubules parallel with one another or as fused tubules having a "donut" configuration. In addition, the crystalloids are nearly identical to configurations which have been described in mitochondrial cristae of the protozoan, Pelomyxa carolinensis.

The anatomy of the parotoid gland in Bufonidae with some histochemical findings. II. Bufo alvarius

The gross and microscopic anatomy of the venom producing parotoid glands of Bufo alvarius has been studied by light and electron microscopy. Histochemical reactions for the presence of venom constituents and of components in biochemical pathways in the synthesis and release of venom were performed. The gland is composed of numerous lobules. Each lobule is an individual unit with a lumen surrounded by a double cell layer. Microvilli of the outer layer interdigitate with microvilli of the inner layer. Cells of the outer layer resemble smooth muscle cells, are rich in adenosine triphosphatase and glucose-6-phosphatase, and contain numerous pinocytotic vesicles, glycogen granules and various organelles. These organelles include "crystalloids" of what seem to be highly organized agranular reticulum. These outer layer cells probably function in some aspects of venom synthesis, active cellular transport and contraction in the discharge of the secretory product. The inner cell layer demonstrates a positive chromaffin reaction, contains steroid material, various organelles, some pinocytotic vesicles and glycogen granules, and appears devoid of a plasmalemma on its inner surface. This layer is probably involved in venom formation and release via an apocrine type of secretion. Bufo alvarius parotid gland shows significant morphological and histochemical differences from that of B. marinus and more nearly resembles a typical steroid producing organ.

The antecubital organ of the primate slow loris (Nycticebus coucang coucang)

A study of the 'antecubital organ' of the slow loris (Nycticebus coucang coucang), was undertaken in light and electron microscopes. As distinct from other prosimian primates there is a complete absence of interstitial cells in the gland suggesting its different functional role. The acinar cells in the 'antecubital organ', of slow loris contain large number of smooth ER and electron-dense secretory granules. The granules are seen both in the apical region of the cells as well as in their basal cytoplasmic processes. Some of these processes appear to terminate close to a blood capillary. The structural features of the 'antecubital organs' of slow loris suggest that it is a mixed gland of both exocrine and endocrine nature.

Reinvestigation of the fine structure of Reinke's crystal in the human testicular interstitial cell

Testicular biopsy materials of men were examined with the electron microscope equipped with a tilling stage. An optical transformation method was applied for the electron microscope images. An attempt was made to clarify relationships between the contour and the internal pattern of Reinke's crystal in the interstitial cell. The shape of this crystal is a hexagonal prism. Three types of internal patterns are observed in relation to the main planes of the crystal. The crystal consists of 50-A-thick filaments. It is trigonal, a = 300 A, c = 450 A, being similar to catalase crystals studied by X-ray diffraction and electron microscopy (20), but the dimensions are different. Dislocations of Reinke's crystal are also analyzed. In some interstitial cells without Reinke's crystal, specially arranged 50-A-thick filaments are observed. They are similar in arrangement to the pattern within Reinke's crystal, but not so closely compacted. Morphological similarities and dissimilarities between this crystal and other crystal and crystalloid structures are discussed.